1. Field of the Invention
The present invention relates to a method for producing a milk calcium composition which is highly dispersible and tasty, and to a calcium-fortified drink or food product with which this milk calcium composition is admixed.
2. Description of the Related Art
Calcium in milk is drawing attention as a source of high quality, highly absorbable calcium. However, the conventional isolation and purification of calcium from milk for admixing with a drink or food product produces an insoluble calcium phosphate precipitate, which causes a marked deterioration in the quality of the drink or food product. Furthermore, calcium phosphate has an unfavourable taste, which also causes a deterioration in the quality of the drink or food product in terms of taste. Under these circumstances, there are demands to develop calcium materials which are derived from milk and which are highly dispersible, for which various attempts are being made.
Examples of conventional methods for producing such calcium materials derived from milk include a method in which whole milk or skimmed milk is acidified or treated with rennin to remove casein by coagulation and precipitation, the resultant whey or supernatant is treated with a UF membrane to recover a permeate, and then the permeate is neutralized to obtain a calcium component as a precipitate (Japanese Patent Publication No. H3-24191) and a method for producing a calcium component for calcium-fortified drinks, in which the proteins in whey are removed by treating with an ion exchange resin or a UF membrane, then the lactose is crystallized and the solution is concentrated using a UF membrane or microfiltration (MF) membrane in a neutral range to obtain a whey mineral component having a calcium content of 2-8% by weight (Japanese Patent Application Laid-open No. H9-23816).
However, the milk-derived calcium materials thus obtained were not satisfactory as calcium materials to admix with drinks or food products since they were poorly soluble and dispersible, and had an undesirable taste.
In view of the problems in the abovementioned prior art, an object of the present invention is to provide a method for producing a milk calcium composition which is highly dispersible and tasty. Another object of the present invention is to provide a calcium-fortified drink or food product with which the milk calcium composition obtained by this method is admixed.
In the course of an intensive study to resolve the abovementioned problems, the present inventors found that a milk calcium composition which is highly dispersible and tasty could be obtained by adjusting the pH of a permeate containing lactic acid and lactic acid ion, which was obtained by treating whey with a UF membrane or NF membrane, to recover milk calcium as a slurry-like precipitate and then admixing this milk calcium with milk proteins. The present invention was thus accomplished.
In the present invention, a permeate containing lactic acid and lactic acid ion, which is obtained by treating whey with a UF membrane or NF membrane, is any one of the following: (1) a permeate obtained by treating lactic acid whey with a UF membrane or NF membrane, (2) a permeate obtained by treating whey, to which lactic acid or a lactate is added, with a UF membrane or NF membrane, and (3) a solution in which lactic acid or a lactate is added to a permeate obtained by treating whey with a UF membrane or NF membrane.
Whey to be treated with a UF membrane or NF membrane can be either acid whey, cheese whey, lactic acid whey obtained by lactic acid fermentation of milk, or the like. However, acid whey having a high calcium content is preferable because calcium can be recovered in a high concentration. Lactic acid whey is also preferable because there is no need to add lactic acid or a lactate to it.
A permeate is obtained by treating whey with a UF membrane or NF membrane. In the present invention, a UF membrane to be used has a cut-off molecular weight of 1,000-500,000, and a NF membrane to be used has a cut-off molecular weight of 100-5,000, which are generally used in the dairy industry. A UF membrane is preferably used since use of a NF membrane reduces calcium permeability. Further, in order to improve calcium recovery upon the pH adjustment in a later step, it is preferable to concentrate this permeate in advance by treating with a reverse osmotic (RO) membrane or MF membrane or by evaporation.
A permeate is poorly dispersible when its lactic acid concentration or lactate concentration, as lactic acid, is less than 0.02% by weight. Therefore, lactic acid or a lactate is preferably added, if necessary, to make the lactic acid concentration or lactate concentration, as lactic acid, of the permeate to be 0.02% by weight or greater. A lactate to be added can be any lactate, such as sodium lactate or calcium lactate, or mixtures containing such lactates including mixtures with lactic acid. In cases where lactic acid whey is used, the addition of lactic acid or a lactate is not necessary since its lactic acid content is 0.02% by weight or greater (lactic acid whey contains about 0.8% by weight of lactic acid).
Lactic acid or a lactate can be added to either whey or a permeate. However, it is preferable to be added to a permeate because the amount of lactic acid to be added is smaller and the concentration is more easily controlled.
The permeate containing lactic acid and lactic acid ion thus obtained is heated and then its pH is adjusted to recover milk calcium as a slurry-like precipitate.
If the temperature upon the pH adjustment is lower than 30xc2x0 C., lactose simultaneously tends to precipitate so that the purity of milk calcium is reduced and the resulting milk calcium composition is poorly dispersible. If the temperature is higher than 80xc2x0 C., milk calcium reacts with phosphoric acid to form calcium phosphate so that the resulting milk calcium composition is poorly dispersible and the precipitate is difficult to be recovered. Therefore, the temperature is preferably 30-80xc2x0 C., most preferably 50xc2x0 C.
The calcium recovery rate decreases if the pH is below 6.0. The taste deteriorates if the pH is higher than 9.0. Therefore, pH 6.0-9.0 is preferable. For the pH adjustment, alkaline solutions, such as sodium hydroxide, potassium hydroxide, calcium hydroxide, sodium carbonate, and sodium citrate can be used.
Milk calcium thus recovered is highly dispersible presumably because when the pH of the permeate is adjusted to form the milk calcium precipitate, lactic acid and lactic acid ion in whey suppress formation of a hard apatite structure primarily consisting of calcium phosphate through reaction of milk calcium and phosphoric acid.
Then, the recovered milk calcium is mixed with a milk protein component to obtain a milk calcium composition. The milk protein component to be added can be any one of raw milk, skimmed milk, skimmed powder milk, casein materials, whey protein materials, and the like. In cases where powder or solid materials are used, they are added as a solution at an appropriate concentration. Further, presumably, recoagulation of milk calcium is restrained by mixing the slurry-like milk calcium precipitate with a milk protein component and the milky taste is further improved.
A calcium content in the milk calcium composition of less than 2.5% by weight of the total solids has too low quality as a milk calcium composition. If the content is more than 5.0% by weight, milk calcium interacts with milk proteins to cause gelation, which renders the composition poorly dispersible. Accordingly, a content of 2.5-5.0% by weight is preferable.
Since the sodium content in a milk calcium composition has a great effect on the taste, it is desirable that it be of an amount such that log (amount of calcium/amount of sodium)xe2x89xa70.9. The milk calcium composition thus obtained can be used without further processing. Also, it can be frozen to produce a frozen product, or spray-dried or freeze-dried to produce a powdered product to be used as a milk calcium composition.
Since a milk calcium composition obtained in the present invention is highly dispersible and tasty, it can be admixed with a drink or food product. The amount to be admixed is preferably less than 50% by weight since an amount exceeding 50% by weight has an effect on the original taste of the drink or food product.
The present invention will be explained in detail in the following examples.